Copolymers of vinyl acetate, vinyl chloride, and various acrylates have been known for some time as has their method of preparation. U.S. Pat. No. 1,933,052 discloses polymers which include the foregoing components in alternative combinations of components. The acrylic components and vinyl compounds are said however to be employed in equimolar proportions and in any event, in a percentage ratio which contains not less that 20% of acrylic or vinyl components. The patentee suggests employment of the foregoing compositions as intermediate layers for bonding metals, wood, leather, and similar materials together. However, as the patentee notes, where smooth surfaces are to be coated, an initial layer of pure polymerized acrylic ester film is first applied to the smooth substrate before deposition thereon of a mixed polymerization product of the invention, which in a preferred embodiment is composed of 40% vinyl chloride and 60% acrylic methyl ester to provide an elastic intermediate layer over which is disposed a further copolymeric formulation of exclusively polymerized acrylic comonomers. This patent does not propose a formulation, useful in a single application, which will combine desired adhesive capability to smooth metallic surfaces with, at the same time, the protective properties afforded by and typical of vinyl chloride polymers and copolymers.
Other typical terpolymer compositions are disclosed in U.S. Pat. Nos. 3,017,396 and 3,370,050. The compositions described in U.S. Pat. No. 3,017,396 are terpolymers of vinyl chloride, vinyl acetate and alkoxyalkyl acrylate designed for use in vinyl floor tile and for employment in emulsion form for application to fabric, metal and wood to improve their resistance to attack by hydrocarbon solvents. This composition does not manifest any significant metal adhesive property and would not be employed characteristically where this property is a necessary qualification for its use since it contains the alkoxy group, as distinguished from hydroxy group which imparts metal adhesive property to the composition described herein.
U.S. Pat. No. 3,370,050 is directed to interpolymers of acrylate esters and relatively high-boiling vinyl compounds suitable for use in the solution polymerization procedures described therein. Excluded from the compositions of the patent, however, is that most utilitarian of components for use in flexible protective coating compositions, i.e., vinyl chloride, alone or in combination, illustratively, with vinyl acetate. Vinyl chloride would be incompatible with its polymer and thus inoperative in solution polymerization. The most nearly comparable monomer to vinyl chloride, at least structurally of those alluded to by the patentee, is allyl chloride, a compound which enters into copolymerization reactions by a chain transfer mechanism that tends to yield polymers of extremely low molecular weight and widely disparate physical properties from those wherein vinyl chloride is present.
Terpolymers of 86% vinyl chloride, 13% vinyl acetate and 1% maleic anhydride have been described in the Encyclopedia of Polymer Science and Technology, Vol. 14, p. 348, Interscience Publishers, New York, New York (1971) for use in lacquer applications where improved adhesion to metals is desired and reference is made additionally to substitution of acrylic or methacrylic acid for maleic anhydride. These products have not, however, satisfied demand for further improved products of this general character, due, in part, to their marked brittleness at depressed temperatures and their failure to secure the bond necessary in many instances. Furthermore, applications for resins, such as hydrolyzed polyvinyl acetate (i.e., polyvinyl alcohol), as a third component are limited since they have been utilized heretofore only in solution prime coats or adhesion promoters and have not been employed in plastisol or dry blend mixtures.